High Intensity Interval Training (HIIT) for Fat Loss and Endurance

HIIT (High Intensity Interval Training) is famous for being an extraordinarily effective cardio option. In this article we take a look at the scientific evidence to see just how effective it really is. Most people’s goal from cardio is either fat loss or endurance, so we’ll focus on these two factors.

HIIT and Fat Loss

To the right is the result of one experiment comparing HIIT to regular endurance exercise.[1] The chart shows the decrease in 6 skinfold body fat measurements after 4-5 months of HIIT or regular endurance exercise. In numerical terms, the endurance exercisers reduced their 6 skinfolds by a total of 4.5mm, while the HIIT group reduced their fat by 13.9mm (210% greater fat loss as measured in mm).

In percentage terms, the endurance group decreased their skinfolds by 5.7% while the HIIT group decreased their skinfolds by 14.8%. A 14.8% reduction in skinfolds will make a clearly visible difference to a person’s body composition. So put simply, HIIT is roughly 3 times as effective as regular cardio for fat loss.

This fat burning benefit of HIIT is likely attributable to the fact that high intensity exercise burns more body fat post-exercise than lower intensity exercise as seen in the chart below.[2]

HIIT and Endurance

One study found similar improvements in heart function from 25 minutes of HIIT as 90-120 minutes of endurance exercise.[3] A second study found that HIIT was somewhat more effective than endurance training for improving VO2 Max with both groups training for the same amount of time.[4]So for endurance, HIIT may be superior to moderate intensity continuous cardio, but the evidence is not conclusive.

Conclusion

HIIT is very effective for reducing body fat.

HIIT is somewhat effective for improving endurance.

Warning: If you have not exercised in a long time, don’t jump straight into intense HIIT. Start out slowly and work your way up to avoid any serious health risks.

Daniel has a strong interest in evidence supported fitness training, preparation and supplementation. His goal is to provide clear information that simply works. He's currently 16 kg of muscle above his starting weight (7kg in the past 12 months), and targeting a continued growth rate of 5kg+ per year.